Imam Al-Baqir (peace be upon him) has said: “The prayer that is offered by a person, sometimes half of it ascends upwards, while at other times it is only one-third, or one-fourth or one-fifth that ascends. Only that portion of the prayer which the person has offered with concentration and mindfulness of the heart is made to ascend. (And so) the people have been ordered to offer the recommended prayers so that they can make up for what has been left incomplete of their obligatory prayers.”
Al-Haqa’iq, Page 219